The invention relates to a system and method for controlling fuel injection of fuel injectors in an internal combustion engine.
A prior fuel injection system includes a common fuel rail and a plurality of fuel injectors in communication with the fuel rail for injecting fuel into a plurality of cylinders of an internal combustion engine. Each of the fuel injectors has an electronic control valve or solenoid for controlling fuel injection into a particular cylinder. An electronic control unit, or controller, is used to control the electronic control valves, as well as other aspects of the fuel injection system. The controller may include volatile and non-volatile memory, input and output driver circuitry, and a processor capable of executing one or more stored instruction sets. In operation, the controller determines an excitation or energizing duration for each control valve corresponding to current engine conditions. Energizing of a particular control valve causes the valve to open, which allows fuel injection to occur. However, imprecise determination of energizing durations may result in operating problems such as engine noise and excessive engine emissions.
A prior method for determining energizing durations by a controller involves determining a desired injection pressure and a raw injection duration from two separate, but interdependent, look-up tables that each reference desired engine torque and engine speed. The raw injection duration is not based on time units, however, but rather is based on angular displacement of the engine crankshaft measured in degrees. The raw injection duration is then adjusted to establish a final injection duration based on injection pressure error, which is a function of desired injection pressure and observed or actual injection pressure. Finally, the final injection duration is converted from degrees to time to establish an energizing duration, and a corresponding control signal is sent to a particular fuel injector.
Because this method involves interdependent look-up tables for determining desired injection pressure and raw injection duration, calibration of the look-up tables and associated controller is difficult and time-consuming. Furthermore, desired injection pressure values, which are used to control a fuel pump, cannot be independently varied so as to optimally adapt injection pressure to variable operating conditions such as air temperature.
Several methods have been proposed to enhance fuel injection capabilities. One such method is known as split injection. Split injection consists of a first injection, called the pilot injection, followed by a delay, and then a second injection, referred to as the main injection. When performing split injection, precise determination of energizing durations for both the pilot injection and the main injection is essential. Many times, operating conditions at which split injection may be performed are restricted to lower engine speeds due to difficulties in establishing precise energizing durations.
A method for determining pilot and main energizing durations is similar to the method previously described. The method involves determining a desired injection pressure based on a desired engine torque output and engine speed, determining a raw pilot injection duration based on a desired pilot engine torque output and engine speed, and determining a raw main injection duration based on a desired main engine torque output and engine speed. As in the above method, the raw injection durations are not based on time units, but rather are represented in degrees of rotation of the crankshaft. Furthermore, the desired injection pressure and the raw injection durations are determined in parallel from separate, but interdependent, look-up tables. The raw pilot injection duration and the raw main injection duration are then adjusted to establish a final pilot injection duration and a final main injection duration, respectively, based on injection pressure error. Next, the final pilot injection duration and the final main injection duration are converted from degrees to time to establish a pilot energizing duration and a main energizing duration, respectively, and corresponding control signals are sent to a particular fuel injector.
It is therefore an object of the invention to provide a method and system for controlling fuel delivery from a fuel injector based on energizing durations that are more precisely determined as compared with prior methods and systems.
Another object of the invention is to provide a method and system for determining energizing durations in time units independently of angular measurements associated with an engine crankshaft.
Another object of the invention is to provide a method and system for determining energizing durations based on desired fuel quantities per injection cycle, mapped against engine speed and desired torque, and actual or observed fuel pressure.
A more specific object of the invention is to provide a method and system for controlling fuel pressure based on desired injection pressure, wherein the desired injection pressure is determined independently of the desired fuel quantities per injection cycle. Preferably, the desired injection pressure can be adjusted independently of the desired fuel quantities per injection cycle in order to account for dynamic engine operating parameters.
Under the invention, a method for controlling fuel delivery from a fuel injector includes determining a first desired engine torque output; determining engine speed; determining a first quantity of fuel to be delivered by the fuel injector based on the first desired engine torque output and the engine speed; determining an injection pressure; and determining a first amount of time for energizing the fuel injector in order to deliver the first quantity of fuel based on the injection pressure.
According to a feature of the invention, the method may also include determining a desired injection pressure independently of determining the first amount of time, and controlling a fuel pump system for supplying fuel to the fuel injector based on the desired injection pressure. Preferably, the desired injection pressure may be altered independently of the first amount of time based on dynamic engine operating parameters. As a result, the fuel pump system may be effectively controlled to optimize fuel pressure to thereby optimize engine operation.
For a system capable of split injection, the method further includes determining a second desired engine torque output; determining a second quantity of fuel to be delivered by the fuel injector based on the second desired engine torque output and the engine speed; and determining a second amount of time for energizing the fuel injector in order to deliver the second quantity of fuel.
A system is also provided for controlling fuel delivery from a fuel injector having an electronic control valve, wherein the fuel injector is in communication with a fuel rail. The system comprises an accelerator pedal sensor for sensing pedal position, a crankshaft sensor for sensing rotational speed of the crankshaft, and a fuel pressure sensor for measuring fuel pressure in the fuel rail. The system further includes a controller in communication with the accelerator pedal sensor, the crankshaft sensor, the fuel pressure sensor and the electronic control valve. The controller includes instructions for determining a first desired engine torque output based on the pedal position, instructions for determining engine speed based on the rotational speed of the crankshaft, instructions for determining a first quantity of fuel to be delivered by the fuel injector based on the first desired engine torque output and the engine speed, and instructions for determining a first amount of time for energizing the electronic control valve in order for the fuel injector to deliver the first quantity of fuel. Furthermore, the controller includes instructions for generating an output signal for the electronic control valve corresponding to the first amount of time.
The above objects and other objects, features and advantages of the invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in conjunction with the accompanying drawings.